It is known in the art that it is desirable to treat the surface of gold and gold alloy castings for dental crowns and bridges in order to prevent the gasification of the gold or gold alloy during the bonding of porcelain thereto and to improve the uniformity of the color of said gold or gold alloy to make the shade control of the porcelain more facile.
There are commercial products available for this purpose. Jelenko Prima, for example, from J.F. Jelenko & Co., a Division of Penn Walt is a gold powder which is dispersed in propylene glycol prior to use by the dental technician. The viscosity of propylene glycol is fairly low and therefore the resultant dispersions are not easily painted onto the castings, e.g. dripping makes it more difficult to transfer the gold powder to the casting. Sufficient gold transfer cannot be accomplished in a single application. Wilcote available from Wilkinson Gold Co. is a gold powder which is dispersed in glycerine by a dental technician prior to use. Glycerine has a somewhat higher viscosity then propylene glycol but the viscosity of the dispersions is still too low to eliminate the dripping of the dispersion from the brush during painting.
Britecote*, a system available from Ceramco, Inc., Long Island City, New York, consists of a gold cake comprising gold powder, pectin, dilithium tetraborate, stannous chloride, and hydrochloric acid. This cake is broken up and dispersed in propylene glycol. It has been found that during storage this cake changes and becomes difficult to disperse in propylene glycol. It is believed that this change is due to the pectin which being a natural product may vary from batch to batch and with time. In any event it has been found that the gold powder tends to agglomerate in the cake thereby forming dispersions including highly agglomerated particles of gold. Moreover, the dilithium tetraborate must be varied on a batch to batch basis to obtain a suitable viscosity in the presence of the pectin.